1. Field of the Invention
The present invention relates to a process for resolving dl-2,2'-bis(diphenylphosphino)-1,1'-binaphthyldioxide (referred to as BINAPO hereinafter) into optical active isomers.
BINAPO is an intermediate compound for producing 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (referred to as BINAP hereinafter) having the axial chirality which is useful as a ligand of an asymmetric hydrogenation catalyst or asymmetric isomerization catalyst.
2. Description of the Prior Art
Asymmetric synthesis is a comparatively new technical field. There are only a few reports on the production of catalysts for asymmetric synthesis. The production of BINAP is disclosed only in Japanese Patent Laid-open No. 61937/1980.
BINAP as the ligand of a catalyst for asymmetric synthesis should be optically active. It is resolved into d-BINAP and l-BINAP by changing BINAP into a BINAP-palladium complex, obtaining the d-isomer from crystals and the l-isomer from the mother liquor, and decomposing the respective isomers by reduction with LiAlH.sub.4. This process is disadvantageous in being long, having poor yields, and requiring auxiliaries. There are many problems to be solved before this process is suitable for use by industry.
The optical resolution of phosphine oxide was reported by Henri Brunner et al. [Chem. Ber. 114, 1137-1149 (1981)]. According to this report, bicyclo [2,2,1]-heptene-5-2,3-dibis(diphenylphosphorane oxide) is reacted with L-(1)-dibenzoyl-tartaric acid to give a diastereomer, which is difficult to dissolve, and which is subsequently hydrolized to give the l-isomer. Additionally, there was also reported by Meisenheimer et al. [Chem. Ber. 44, 356 (1911), Ann. 449, 213-248 (1926)] the process for producing an optically active phosphorus compound of ##STR1## type from d-camphor-10-sulfonic acid (referred to as d-CSA hereinafter) or d-3-bromocamphor-10-sulfonic acid (referred to as d-BCSA hereinafter). The process requires a long time for crystallization and is very difficult to practice.
Therefore, a need continues to exist for a process for the optical resolution of dl-2,2'-bis(diphenylphosphino)-1,1-binaphthyldioxide which provides excellent yields of the d and l enantiomeric compounds and which can be readily carried out on an industrial scale.